1. Field
Embodiments described herein generally relate to a substrate processing system and related methods, such as an etching/deposition method.
2. Description of the Related Art
The fabrication of microelectronic devices includes a number of different stages, each including a variety of processes. During one stage, a particular process may include imparting a plasma to the surface of a substrate, such as a silicon substrate, to alter the physical and material properties of the substrate. This process may be known as etching, which may involve the removal of materials to form holes, vias, and/or other openings (referred to herein as “trenches”) in the substrate.
Plasma etch reactors are commonly used for etching trenches in semiconductor substrates. These reactors contain a chamber within which the substrate is supported. At least one reactive gas is supplied to the chamber and a radio frequency signal is coupled to the reactive gas to form the plasma. The plasma etches the substrate that is positioned within the reactor. The substrate may also be coupled to a radio frequency (RF) signal to bias the substrate during the etching process to enhance etching performance and trench profile.
These trench profiles often require different critical dimensions. The critical dimensions include width, depth, aspect ratio, resist selectivity, roughness of the sidewalls, and planarity of the sidewalls. These critical dimensions may be controlled by various factors, two of which are etching time and etching rate, which further depend on the materials being etched and the type of etching system being used.
One material of particular importance is silicon. Through silicon via (“TSV”) etching is a unique application that requires a low frequency bias and a low temperature environment to form deep trenches in a silicon substrate. However, during fabrication, the silicon is generally covered by multiple layers of other materials, such as an oxide layer and a metal layer that are deposited on the silicon. Oxides include different etching requirements than that of silicon, such as a high frequency bias. In addition, during deposition, a thin film polymer layer may be deposited onto the layers of the substrate as the trench is being formed to protect the trench sidewalls prior to etching. This polymer layer may further include different etching requirements than the oxide, metal, or silicon layers. These distinct requirements influence and increase the complexity of the type of etching system used.
One type of etching system may include in situ plasma etching. Using this first type of etching system, a trench can be formed by alternating the removal and deposition of material on a substrate in a single reactor with a removing plasma and a deposition plasma. Another type of etching system may include remote plasma etching. Using this second type of etching system, a trench can be formed as in the in situ system, except that the plasmas may be generated in a remote reactor prior to being introduced onto the substrate located in the primary reactor. In addition to the types of etching systems, the process of etching with each system may also vary. Some etching processes employ multi-step approaches, such as a time multiplexed gas modulation (“TMGM”) system or a Bosch system, that includes several recipe steps, such as etch and deposition, or etch, flash, and deposition. The TMGM process etches a material for a period of time and then deposits a protective film upon the previously etched surface to protect the surface, typically the sidewalls of the trench, from further etching. These two steps are defined as a cycle and are repeated as a deeper and deeper trench is formed. The number of cycles in the TMGM process depends upon the required depth of the via and the etch rate of the process. The number of cycles may exceed 1,500 for some processes. Thus it is desirable to decrease each cycle time in order to decrease the cost of ownership.
Further, one critical dimension of particular importance when forming a trench, the roughness of the sidewalls, may render a microelectronic device defective if not properly controlled. During the etching cycles, material is being deposited and removed as the trench is formed. In response, a series of “peaks” and “valleys” may develop along the sidewalls of the trench, a phenomenon known as “scalloping.” Numerous and larger peaks and valleys increase the roughness of the sidewalls of the trenches.
Therefore, there is a need for an improved method and apparatus of an etching system and process which reduces the cost of ownership while maintaining a desired etch profile.